Patent GB-891943-A (GB)
IPC: D02G1/16
Abstract: 891,943. Synthetic filaments. DU PONT DE NEMOURS & CO., E. I. June 10, 1958 [June 11, 1957; May 19, 1958], No. 18582/58. Class 2(2) [Also in Groups VI, VIII, IX and XIV] A continuous extruded or spun shaped filamentary structure of crystalline synthetic polymer comprises a three-dimensional integral plexus composed of a multitude of molecularly oriented film-like and/or ribbon-like elements less than 2 microns in thickness which unite and separate at random intervals along and across the plexus. The exterior surface of such a structure (termed a "plexifilament") may vary from, preferably, that of a smooth monofilament to that of an elongated matted cobweb. The interior is always a threedimensional integral fibrous plexus as described above, but may vary from, preferably, a multitude of ribbon-like fibrils uniting and separating at random longitudinal and cross-sectional intervals throughout the structure to form a three-dimensional network, substantially free of tunnels and cavities, termed a "fibrillous" plexifilament and resembling a staple fibre yarn except that it has no loose ends, to a labyrinth of fine longitudinal tunnels interconnecting at random intervals, termed a "foamy" plexifilament. In an intermediate form, the plexifilament contains no tunnels, but a multitude of closed cavities so that the fine structure resembles a honeycomb or very fine sponge, or both tunnels and cavities may be present. The orientation of the ribbon-like elements may be predominantly in the direction of the longitudinal axis of the structure. Plexifilaments may be twisted, and may be stretched at room or elevated temperatures to effect additional molecular orientation The preferred material is linear polyethylene, plexifilaments made therefrom having tenacities exceeding 13 g./denier, but other materials specified include polyoxymethylene, polyethylene terephthalate, polyhexamethylene adipamide and sebacamide, polycaprolactam, polycarbonates, polyurethanes, polypropylene, poly(iso-butyl ethylene), ethylene copolymers with alkenes or vinyl acetate, polyvinyl chloride, polyvinyl fluoride, acrylonitrile polymers and coplymers, and poly(2,5-dimethyl-2-4-hexadiene). Plexifilaments are made by extrusion of a solution of a crystallizable synthetic polymer, which is at a temperature higher than the normal boiling point of the solvent and high enough to cause substantial bubble nucleation when the pressure is reduced to atmospheric, and which is under autogenous or higher pressure, through an orifice into a region of lower pressure, suitably air at normal atmospheric pressure, the solvent preferably being substantially removed without the application of external heat. The process is termed "flash-spinning" by analogy with flashdistillation. The spinning solution may contain 5-70% by weight of the polymer, preferably 5-30%, and the normal boiling point of the solvent should be at least 25‹C. below the softening point of the polymer. Where linear polyethylene is spun, the solvent may be a chlorinated or fluorinated hydrocarbon, e.g. methylene chloride, or cyclohexane may be used. Solvents used may be liquid or gaseous at room temperature, and the solvent used varies with the polymer spun. Those specified include benzene, toluene, butane, pentane, hexane, heptane, octane, carbon tetrachloride, chloroform, methyl and ethyl chlorides, alcohols, esters, ethers, ketones, nitriles, amides, sulphur dioxide, nitromethane, and water. Polymerization to produce the polymer may be carried out in the spinning solvent, which may contain conventional additives, and spinning may be carried out batchwise or continuously. Suitable spinnerets are shown in Figs. 7, 8 and 9, that of Fig. 9 being such that the solution can expand in a controlled manner before leaving the orifice. The rate of generation of the plexifilament may be 5,000 yards/min. or more. Plexifilaments so made have a very high covering power owing to their reticulate structure, and in the as-spun state are molecularly oriented. Their physical properties compare favourably with conventional filaments of the same materials, especially after stretching. After-treatments described include treatment with phosphorus trichloride in the presence of oxygen, or chlorosulphonation, to improve dyeability and electrostatic properties, and stretching under various conditions of temperature and draw ratio, depending on the polymer used. Stretching changes the appearance of the plexifilament, which becomes a lustrous, strong, flat, white, continuous unitary structure having the appearance of a continuous multifilament yarn. By blowing air through it or in other conventional manner, it can be worked into a round fluffy, yarn-like material.